1. Field of the Invention
The present invention relates to a fiber fuse stopper (fiber fusion preventing device) that protects fiber waveguides or components in a system in which high-power light is transmitted through a fiber waveguide, for example, in the fields of optical communications, laser beam machining, or the like.
2. Description of Related Art
In recent years, a significant increase in the transmission capacity of communication paths has been achieved in the field of optical communications. With this increase in transmission capacity, the intensity of the light propagating through optical fibers or optical devices has been increased. Such intensified light has created new problems in that minute dust particles or the like that are attached to the optical coupling ends may cause “fiber fuse, ” namely, melting of affected portions of the fiber and subsequent fusion thereof to adjacent components. Fiber fuse can result in destruction of not only the optical transmission path but also optical devices or apparatuses connected thereto (see Seo et al., 2003 Society Conference of IEICE/the Institute of Electronics, Information and Communication Engineers, p. 321; Seo et al., National Fiber Optics Engineers Conference, 2003 Technical Proceedings, p. 22–30; Maeda et al., 2003 Society Conference of IEICE/the Institute of Electronics, Information and Communication Engineers, p. 320; D. P. Hand and P. St. J. Russell, OPTICS LETTERS, Vol. 13, No. 9, September 1988, pp. 767–769, for example).
In order to solve such problems, a technique has been proposed that is described in Japanese Unexamined Patent Application, First Publication No. 2002-372636. In the technique described in Japanese Unexamined Patent Application, First Publication No. 2002-372636, fiber fuse is prevented by providing a core-enlarged portion in some region of an optical fiber to enlarge the mode field diameter (MFD) so that the optical energy density is reduced.
However, the technique described in Japanese Unexamined Patent Application, First Publication No. 2002-372636 has the following shortcomings:
When an optical fiber is heated to enlarge the core thereof, the fiber is required to be heated to a relatively high temperature for a relatively long time, which disadvantageously incurs an increase in the manufacturing cost. In addition, the strength of the fiber may be reduced because the coating of the optical fiber must be removed in a central region of the fiber, and because the optical fiber is heated. As a result, the optical fiber may become prone to breakage under normal operating conditions, which may decrease the reliability of the entire system. Furthermore, providing reinforcing members for reinforcing the region of the fiber in which the strength is reduced may incur an increase in cost.
Two factors are responsible for fiber fuse: increased optical energy of light propagating in cores and conduction of heat. The allowable light intensity of the system is limited since the above-described technique can reduce the factor of the optical energy in cores while it cannot address the factor of thermal conduction. In addition, in a typical optical fiber, such as a single-mode optical fiber, since the achievable enlargement of the mode field diameter (MFD) by the diffusion of dopants is three times the original size at best, the reduction of the optical energy density is one ninth at maximum. Thus, the reduction in achievable optical energy density is limited, and applications of this technique are accordingly limited.
Furthermore, in the above-described technique, an optical fiber having a core enlarged portion at the center thereof is provided, and optical connection means are provided at the two ends of the optical fiber for connecting to a transmission line or to a transmission unit or device. This adds an additional junction, which may incur splice loss or disadvantage in production costs. In addition, if the optical fiber is connected to a transmission unit in a housing external to the transmission unit, an enlarged footprint for the installation the external housing is required. Furthermore, in a case in which the connection is achieved within an apparatus, replacing fiber fuse stoppers (fiber fusion preventing devices) requires considerable labor if fiber fuse occurs.
In addition, the above-described technique has further shortcomings as follows:
As described above, two factors are responsible for fiber fuse: increased optical energy of light propagating in cores and conduction of heat. The allowable light intensity of the system is limited since the above-described technique can reduce the factor of the optical energy in cores while it cannot address the factor of thermal conduction. One study reports that optical fibers can withstand light intensity up to 10 GW/cm2 or higher, and to prevent fiber fuse, removal of heat may be more effective than reducing the optical energy density. In addition, in a typical optical fiber, such as a single-mode optical fiber, since the achievable enlargement of the mode field diameter (MFD) by the diffusion of dopants is three times the original size at best, the reduction of the optical energy density is one ninth at maximum. Thus, the reduction in achievable optical energy density is limited, and applications of this technique are limited.
When an optical fiber is heated to enlarge a core thereof, the fiber is required to be heated to a relatively high temperature for a long time, which disadvantageously incurs an increase in the manufacturing cost. In addition, the strength of the fiber may be reduced because the coating of the optical fiber is removed in a central region of the fiber and because the optical fiber is heated. As a result, the optical fiber may become prone to breakage under normal operating conditions, which may decrease the reliability of the entire system.